The present invention is related to a hand tool, and more particularly to a torque wrench in which the action force at the force application end of the wrench is equal to the action force at the resistance end. Even if the wrenching position of wrenching the wrench is varied, the action force at the force application end will still conform to the action force at the resistance end.
The existent torque wrenches can be divided into mechanical type wrenches and electronic type wrenches. A torque value can be set in a mechanical type wrench, in the case that the torque applied to the wrench exceeds the set value, an alarm such as a sound is emitted. An electronic type wrench is able to display the wrenching torque.
Both the mechanical type wrenches and electronic type wrenches have a common shortcoming, that is, the force applied to the wrench is unequal to the wrenching force acting on a socket or a screwing member.
FIG. 1 shows a conventional mechanical torque wrench 10 having a tubular body 12 and a bar body 13 disposed in one end of the tubular body 12. The bar body 13 is pivotally connected with a front end of the tubular body 12 via a pin 14. The front end of the bar body has a head section 15. When rotating the handle 16 of a rear end of the tubular body 12, the handle 16 drives a slide block 20 to move via an adjustment mechanism 18 so that a spring 22 resiliently abuts against a push block 24. A front end of the push block resiliently abuts against the rear end of the bar body 13. The resilient energy is right the set value of the wrench.
The head section 15 is fitted with a socket or a screwing member and then the wrench is wrenched to wrench the socket or the screwing member. When the wrenching force applied to the wrench is greater than the set value, the bar body 13 slips off from the push block 24 to emit a sound. This informs a user that the applied force exceeds the set value.
The above wrench is a single-fulcrum structure, that is, simply the pin 14 serves as the fulcrum 14 between the application force end (the handle) and the resisting force end (the head section) of the wrench. FIG. 2 shows the static state of such single-fulcrum structure. It can be known from the bending moment that the torque at the position of the applied force P is unequal to the torque at the fulcrum R. Therefore, the action forces at the resisting force end and at the application force end of the wrench are unequal. As a result, the wrenching force applied to the wrench is unequal to the wrenching force applied to a screwing member by the head section. FIGS. 2 and 3 respectively show diagrams of bending moment (M) and shear force (S) at different force application points.
Similarly, the conventional electronic torque wrench only has one fulcrum. The action force at the resisting force end is unequal to the action force at the application force end of the wrench. The displayed torque value is hardly true and reliable.
In addition, with respect to the single-fulcrum torque wrench, when the position of the wrench, to which the wrenching force is applied is varied, the position where maximum deformation takes place is also varied. However, the tension gauge of the electronic torque wrench for measuring the deformation is arranged in a fixed position; also, the slippage structure of the mechanical torque wrench is arranged in a fixed position, therefore, the measured position is often not the maximum deformation position. Accordingly, the result of the measurement is hardly true and accurate. With respect to mechanical torque wrench, there is often a difference between the set torque value and the true wrenching force.